A turbomachine has a principal direction extending along a longitudinal axis, and typically comprises, from upstream to downstream in the gas flow direction, a fan, a low-pressure compressor, a high-pressure compressor, a combustion chamber, a high-pressure turbine and a low-pressure turbine including in particular an exhaust housing. The exhaust housing contributes to delimit the primary channel of fluid (or gas flow) passing through the turbomachine, and ensures, through the bearing supports, the concentricity between the rotor and the stator of the turbomachine, as well as the connection of the downstream end of the motor to the nacelle. The exhaust housing is therefore one of the principal structural parts subject to very high heat levels, and wherein pass extreme unbalanced loads.
This exhaust housing includes conventionally:                a hub, centered on the axis of the turbomachine,        an external frame, coaxial with the hub, and        a set of arms, or sleeves, connecting the hub and the external frame.        
The hub generally comprises a flange (with very diverse shapes) connected, at an internal part, to one (or to some) bearing support(s) intended to center the rotor on the axis of the turbomachine, and at an external part, to the exit cone (or exhaust cone, or “plug”), via an attachment strut. This flange is moreover covered with a sheet-metal part delimiting the channel, in its lower portion, and having openings adapted for receiving the arms.
These hubs are traditionally of a shape that is not or is only slightly deformable (called Y or H, among others), and this type of architecture induces strong forces in the rest of the housing, for example, at the intersection between the leading edge of the arms and the flange(s). Moreover, when the turbomachine is operating, the exhaust housing is subject to high temperatures and to very high thermal transient gradients. This is particularly the case of the hub, between its lower portion, that is at its bearing support attachment struts, and its upper portion, that is at its duct plate. Finally, the hub must be capable of supporting, in terms of ultimate strength, the forces and moments resulting from the loss of a blade.
It is therefore necessary that the hub be sufficiently rigid. However, it must also be capable of mechanically accepting a sufficient internal deformation (or, if it is associated to tangential arms, a free rotation about the axis of the housing), to be able to ensure the overall lifetime of the exhaust housing.
Considering the rigidity of the hub, loads due to strong transient thermal gradients (average and/or local temperature excursions) are displaced toward the outer frame and particularly to the leading and trailing edges of the arms. However, in making the exhaust housing hub more flexible to distribute the deformations and to limit the forces applied to the different parts which constitute it, it is made more sensitive to its outside environment in the turbomachine, in particular in vibration and under extreme loads. It is therefore necessary to maintain a minimum rigidity so that it remains stable and robust even in the case of a change in mechanical and vibratory constraints, even in case of a change in mechanical and vibratory forces undergone by the turbomachine (modification of thermal fields, of extreme loads, etc.).
It is therefore sought to propose a hub which is at the same time capable of compensating the thermal dilations and to homogenize the radial deformations over 360° at the intersection of the inner channel wall and the leading edge of the arms, without however impeding the deformation of the rest of the exhaust housing, so as to prevent the premature decay thereof.
Solutions proposed at present are not generally applicable to all types of turbomachines, because they often require the addition of parts, which represent both an additional cost and a non-negligible mass, are too complex to be implemented, or are too voluminous.
For example, in order to compensate the relative dilations of the different parts of the housing, it has been proposed to tangentially rather than radially integrate the arms between the hub and the outer frame. In this manner, during the relative dilations of the parts due to thermal gradients in the exhaust housing, the hub turns with respect to the outer frame, which allows it to avoid punching by the arms and the risk of perforation of the external frame by different relative deformations between two or several adjacent parts. However, in certain exhaust housings, the distance between the hub and the outer frame is very short, which limits the possibility of implementing such tangential arms. This solution can therefore not be considered for all types of turbomachines.
It has also been proposed to make the duct plate and the flange in two distinct pieces, so as to allow their relative movement during thermal dilation of the operating parts and to thus reduce the forces applied to them and at their intersection with the arms. However, the separation of the duct plate and the hub involves the use of additional fixing means, such as flanges and nuts, which increases the size of the hub and thus increases the overall weight and cost of the housing. Significant leakage of the flow in the interstices may further result from this embodiment. It remains therefore a need for some exhaust housings to form the flange and the duct plate integrally, that is to say in single piece.
There has also been proposed, in document JP 09 324699, a hub of a housing of a turbomachine including an inner channel wall, from which extend vanes and a connecting wall with a curved shape intended to connect the inner channel wall to an internal attachment strut. However, the curved shape proposed by this document forms an obstacle to flow likely to cause local aerodynamic perturbations. Moreover, the concavity in the central part of the connecting wall forms a cavity likely to generate parasitic thermal gradients that are very harmful at these temperature levels.